WASHINGTON — The Army made critical mistakes in tests of a new body armor design, according to congressional investigators who recommend an independent review of the trials before the gear is issued to troops in Iraq and Afghanistan.

The Government Accountability Office report says the Army deviated from established testing standards and concludes that several of the designs that passed would have failed had the tests been done properly.

The Army has ordered about 240,000 of the new type of bullet-blocking plate to be used in ballistic vests, but doesn”t plan to rush the armor into combat. The Army says the plates will be stored until needed to meet future demands.

In a lengthy response to the GAO report, Defense Department officials reject the call for an outside look. The officials acknowledge there were a few problems during testing of the bullet-blocking plates. But these were minor miscues, they said, that don”t shake their confidence in the overall results.

Given the military”s opposition to an external review by ballistics experts, the GAO says Congress should decide whether such a step is necessary.

In a letter sent Friday, Reps. Neil Abercrombie, D-Hawaii, and Roscoe Bartlett, R-Md., urged Army Secretary John McHugh to follow the GAO”s recommendations. They did not, however, say what they would do if McHugh doesn”t.

Abercrombie is chairman of the House Armed Services air and land forces subcommittee; Bartlett is the panel”s top Republican.

The GAO report is the latest study to call into question the Army”s ability to oversee the production of a key piece of battlefield equipment.

In January, the Pentagon”s inspector general faulted the Army for not properly overseeing a series of tests on an earlier model of the protective plates at a private ballistics laboratory.

The inspector general”s audit recommended that nearly 33,000 plates be pulled from the Army”s inventory of nearly 2 million because the inserts might not provide troops with adequate protection against armor-piercing bullets. The Army disputed the findings, but withdrew the plates as a precautionary step.

Stung by the inspector general”s conclusions, Army officials dismissed the private laboratories they”d long relied upon for the tests and said they would do the vital job themselves at a military testing facility in Aberdeen, Md.

That proved to be a contentious decision, however. The testing companies and manufacturers of the plates insisted the private sector could do the trials better, faster and for much less money.

With the GAO report, that argument is sure to get new traction.

In their letter to McHugh, Abercrombie and Bartlett said the move may have been “premature.” They want him to review why the Army would exclude independent, private laboratories, which are certified by the National Institute of Justice, from the testing.

The testing at issue took place last year. Companies that passed were awarded contracts potentially worth $8 billion to manufacture an improved plate design.

The body armor used by most American forces consists of a ballistic vest with two large, specially hardened ceramic plates that protect most of the upper body from enemy bullets and shrapnel.

The plates and vests go through demanding tests during the design phase. Later, after production begins, sample plates are shot at on ranges to ensure there has been no deviation from the specifications. These so-called “lot acceptance tests” require a quick turnaround so manufacturers can keep their production lines moving.

The GAO says the Army”s most significant departure from testing standards was the incorrect measuring of the amount of force a plate can withstand. Correctly calculating this is important because the depth of the indentation on the plate shows the amount of blunt force trauma to the soldier.

Army officials have maintained the criticism of their testing and oversight of body armor is overblown. They note that no U.S. troops have been killed in Iraq and Afghanistan because their body armor was flawed and failed to protect them.

In the 25-page response to the GAO report, the Pentagon says the Army has made a heavy investment to ensure body armor testing is done carefully and accurately.